There are some specific aspects of sign ballasts that bear mentioning. UL concerns, sign ballast selection and application and installation factors are discussed below.
Sign ballasts incorporate a number of symbols and notations on their label that are easily recognized. There may be markings on the label that are not self-explanatory, such as Class “P”, Type 2 and HL. These are United Laboratories (UL) designations that indicate that the ballast meets certain industry requirements.
For the past few years, sign ballasts have been equipped with UL class “P” thermal protection. Class “P” is a requirement of UL standard 2161. Ballasts labeled with class “P” use an internal device that disconnects the ballast from the supply line if the internal temperature of the ballast coils reaches 105 degrees centigrade. Once the ballast cools down, the device automatically resets and normal operation resumes. If ballast is thermal cycling (repeatedly turning on and off as it heats up), it is due to excessive heat. The trigger could be high voltage fluctuations, loose ballast mounting, ballast approaching end of life or other causes.
Sign ballasts are generally manufactured using “UL Type 2 Outdoor” cans. A Type 2 can has a special coating to resist rust. The Type 1 can, used for general lighting applications, does not. Type 2 cans may be used in plastic sign applications without putting the ballast in a separate metal enclosure. “Type 2” does not mean weatherproof, but they do provide some moisture resistance.
Another UL marking on many sign ballasts is “HL”. The HL notation means that the ballast has no sparking components exposed to the air and is suitable for use in hazardous locations. “HL” is a typical requirement in the petroleum industry. All sign ballasts manufactured by Universal Lighting Technologies are UL class “P”, Type 2 and HL listed.
Choosing the Correct Sign Ballast
Selecting the proper sign ballast for your plastic sign application should be a relatively easy task. The normal sign ballast is rated for 120-volt input and operates 800 mA high output (HO) T12 lamps. Sign ballasts also are available for slim-line lamps or other voltages such as 277, however the vast majority of the installations are 120 volt HO. Typically lamps are operated in series (six lamp ballasts are two three-lamp series circuits, in parallel). With series wiring, the lamps are part of the circuit, so if one lamp fails, none of the lamps on that circuit remain lit. In signs using multiple ballasts, adjacent lamps will often be operated by different ballasts to avoid a large dark spot should one lamp fail.
The variables used to select the proper ballast are the number of lamps being operated and the total lamp footage. For example, the Universal Lighting Technologies’ Sign aÔ sign ballast 256-448-800 will operate any one-, two-, three- or four-lamp combination of T12 800 mA lamps covering 8 (minimum) to 16 feet (maximum) total lamp footage.
选择合适的电源取决于你使用灯的数量与总长度，例如，照明技术公司 Sign aÔ sign的电源256-448-800可用于任何一盏、两盏、三盏或四盏T12 800 mA灯的组合，最小覆盖8英尺，最大16覆盖英尺。
Economies of scale and application are important in selecting the proper sign ballast. Sign ballasts have wide application ranges that often overlap. For example, Universal Lighting offers five different ballasts that operate two four-foot lamps. However, the most economical choice is the SignaÔ sign ballast 256-248-800, which is rated for any one or two lamp combinations of T12 800 mA lamps with total lamp footage of 3 (minimum) to 8 feet (maximum) lamp coverage. As a general rule, the most economical choice is to select the ballast where the actual application matches the maximum limits of the ballast. A ballast for one or two-lamps is generally less expensive than a ballast for one-, two-, three- or four-lamps, and a ballast that operates up to 16 feet (maximum) is less expensive than one that operates up to 24 feet. Choose the closest match as long as you don’t exceed the published lamp footage range.
The lowest cost ballast option may not always be the most practical. Using sign ballasts that operate many applications can simplify inventory needs and reduce costs. As long as the actual application is within the ballast’s published range, you can be confident with its performance. If the lamp application is listed on the ballast label, then it has met and passed all of the UL testing requirements.
Do not experiment by using a ballast that you happen to have in stock in an application slightly outside of the performance range. The sign could perform fine in the shop, however you’re asking for trouble in the field. Using a non-listed combination of lamps will void the UL coverage. Ballast overheating, excessive lamp end blackening, hard starting, short lamp life or short ballast life are a few of the possible field problems caused by using a ballast that is not rated for the application. Typical service calls for a plastic sign cost several hundred dollars. Saving a few dollars by using a “close enough” ballast is not wise in the long run.
Application and Installation Factors
Temperature has a critical impact on the performance of a sign. Light output is a factor of the mercury vapor pressure inside the bulb. The colder the lamp is, the lower the light output. Cold lamps are also more difficult to start. Magnetic sign ballasts are rated for reliable starting down to minus 20 degrees Fahrenheit. At temperatures below that, it can be difficult to start the lamps.
Another factor that can cause erratic starting is a poor ground. More importantly, grounding provides added safety. Sign ballasts are designed under UL standards for protection from shock hazard, however certain conditions of ballast failure at end-of-life can result in shorts. An ungrounded sign is a potential hazard and can give misleading symptoms when looking for sign faults. Always disconnect the power before servicing a sign. Service work should only be performed by qualified personnel and in compliance with OSHA guidelines for safe electrical practices.
The two main enemies of the ballast are heat and moisture. The ballast will generate heat during operation and by design should not exceed 90 degrees centigrade at the hottest spot on the ballast case. Higher operating temperatures will shorten the ballast life and could result in thermal cycling. To maintain normal operating temperatures, the ballast should be mounted against a flat surface of heavy gauge metal, such as a structural part of the sign, and it should be mounted far away from other sources of heat, such as other ballasts and lamps. A lamp will generate about three-fourths of the heat in a plastic sign. The ends of the lamp are the hottest part, so the ballast should be mounted as far away from the lamp ends as possible. To help reduce moisture the sign should be well vented without allowing water to enter.
电源的两个主要敌人是热量和湿气。 电源在运行期间会产生热量，并且设计在电源箱的最热点处不应超过90摄氏度。 较高的工作温度会缩短电源寿命，并可能导致热循环。为了保持正常的工作温度，电源应安装在重型金属的平面上，例如标识的结构部分，并且应安装在远离其他热源的地方，例如其他电源和灯。灯在塑料标识中产生大约四分之三的热量，灯的末端是最热的部分，因此电源应安装在尽可能远离灯端的位置。为了减少水分，标识应及时通风，避免水气进入。
High or low line voltage can have a major impact on the life of the sign components. Low voltage does not generally impact a ballast life, yet it can result in inadequate filament heating during starting, shortening lamp life. High line voltage can result in shortened life for both the ballast and the lamps. It is recommended that corrective measures be taken if the voltage is less than 110 or higher than 125 on a nominal 120 volt circuit.
That’s a quick thumbnail sketch of what a sign ballast is, and some application issues that might arise. It is important to recognize that the sign industry and its governing body are anything but static. Restrictions on the size of signs are commonplace and limits on energy consumption are starting to be enacted. Overall, the industry is changing with the times. Over the last few years, there has been a shift in product mix towards the smaller ratings and an increased interest in the use of alternative lamps, such as the T8 high output. Electronic sign ballasts also are growing in popularity. These developing products show a great deal of promise and will become more important as our industry and the application installation challenges continue to evolve.